I think we need to remember there is more than a binary liberal/conservative choice.
Social and economic ideology is often split. One's authoritarian/libertarian stance is very important. "Gun control" is rather inherently authoritarian. It basically says, "the government doesn't trust you with this power, so you must give it up." I think we need to examine WHY we desire to give the government certain authorities to limit our rights, and where we draw the line.
The only way I seem to be able to understand a "liberal" (meaning libertarian on social policy here) supporting gun control would be to invert the perspective. If one views gun control as affecting the other party, it becomes more attractive. If person A doesn't own a gun, keeping BG Y from having one would increase person A's ability to make free decisions. Sadly, this leads people to support restrictive policies inconsistent with their stated philosophy.
...unless one assumes "liberals" are authoritarian in nature. Given current economic policy, this may be true, but it does not match with "classic liberalism" nor the DNC's social goals...
It's an odd paradox to me.